As depicted in the example shown in FIG. 1, the nanoparticles described herein are each made up of a group or a collection of several polymer chains that are organized around a center 1. The polymer chains are linked together at one end at a core formed from cross-linked monomer units on each polymer chain. The polymer chains extend from the core 2 outwardly to form a shell 3. The shell 3 includes the monomer units of the polymers that are not in the core 2. It should be understood that the shell 3 is not limited to a single monomer unit in each polymer chain, but may include several monomer units. Additionally, the shell 3 may be separated into sublayers, and the sublayers may include blocks of various homopolymer or copolymer. For example, a sublayer may include a block of randomized styrene-butadiene copolymer or a homopolymer such as butadiene. The outermost layer of the shell 4, is comprised of the monomer units or functionally or non-functionally initiated polymer chain heads at the outer terminal ends of each polymer. The shell 4 is the outermost portion of the nanoparticle. The living polymer chains form micelles due to the aggregation of ionic chain ends and the chemical interactions of the polymer chains in hydrocarbon solvent. When the multiple-vinyl aromatic monomer is added, the micelles become crosslinked and the stable nanoparticle is formed.
Nanoparticles and liquid polymers for use in rubber compositions are known from commonly owned U.S. patent application Ser. No. 11/305,279, which is hereby incorporated by reference. The combination of nanoparticle and liquid polymer improves important properties of rubber articles, such as vehicle tires, and in particular, the tread portion of vehicle tires. For example, wet/dry traction and rolling resistance of tire tread can be improved with the addition of nanoparticles and liquid polymers while maintaining good reinforcement for tread durability. A reduction or elimination of the amount of processing oils needed in a composition used for vehicle tires, and this is made possible by the liquid polymer and nanoparticle rubber composition.
However, there are difficulties in synthesizing and processing the previously disclosed nanoparticles and liquid polymers. Previously known methods involve synthesizing nanoparticles and liquid polymer separately, drying them separately, and then separately adding each component into a rubber composition. The nanoparticles suffer from poor dispersion in the rubber compound and the liquid polymer is difficult to process. Processing problems stem from the fact that the liquid polymer is a highly viscous substance that is very difficult to separate from solvent and dry. The two separate components also have to be stored separately, thereby consuming valuable inventory space.